The energy embodied in aluminum
From TheConversation.com (never heard of it, but it seems like a good news source): the embodied energy of aluminum is 211 gigajoules per ton. It takes a lot of energy to separate aluminum from its ore but it is relatively easy to recycle (relative to other metals like steel). Embodied energy is a large part of ecological impact. A hybrid car may get better gas mileage than a conventional car but it took a lot of energy to mine and process the precious metals that make up batteries and electrical motors. Likewise a building is judged both on how much energy is needs to operate and how much energy it needs (in the embodied energy of the raw materials and the energy of the construction process) to get built. Lots of different tools and programs exist to help qualify and reduce the ecological footprint of a project.
[My first job in an architectural setting involved helping to build a presentation model of the Pearl River Tower, billed as the first ‘Net-Zero Skyscraper‘ at the time of design. It’s usually hard to find independent verification of such performance after a project is built.]